Artificial nail and gel-based cosmetic compositions are known. Artificial nails are widely used by women who desire to have long, attractive fingernails that do not break or chip as readily as natural nails. Further, gel-based nail polishes have become increasingly popular in recent years, as they may provide improved properties over conventional nail polishes, such as extended wear and improved shine. However, gel-based nail polishes and compositions for artificial nails are traditionally cured using UV radiation, which may be time-consuming and/or may damage the cosmetic film and/or nail bed.
In recent years, ultra-violet light emitting diodes (UV-LEDs) have been used as an alternative to conventional UV light sources for curing photocurable resins, due to their reduced power consumption and significantly increased lifespan. For instance, the bulbs in UV-LED devices generally do not need to be replaced, making UV-LED devices more cost-efficient. UV-LEDs generally have a single peaked wavelength distribution, for example, at a wavelength ranging from about 380 nm to about 430 nm. In contrast, UV lamps have a peaked distribution at a wavelength ranging from about 250 nm to about 400 nm. The use of UV-LED lamps having a higher wavelength may result in decreased damage to the cosmetic film and/or nail bed relative to that caused mainly by UV light with a shorter wavelength and higher energy.
Further, the use of UV-LED lamps may increase efficiency, for example, by reducing curing time, which thus reduces the amount of time a consumer has to spend having their nails “done.” Table 1 below provides a comparison of the time required to cure UV gel-based nail polish, using both UV and UV-LED light sources. As seen in Table 1, gel-based nail polishes can be cured using UV-LED radiation at a significantly reduced curing time. Thus, there is a desire in the cosmetic industry to provide consumers with safer and/or more convenient photocurable cosmetic products that can be cured with UV-LED.
TABLE 1Exemplary Photocuring Times withUV and UV-LED Light SourcesNail Polish LayerUV lightUV-LEDGel Base Coat10sec30secGel Color Coat 12min30secGel Color Coat 22min30secGel Top Coat2min30secTotal Time6 min 10 sec2min
However, UV-LED is deficient in light with a short wavelength, for example, wavelengths shorter than about 300 nm, or wavelengths shorter than about 350 nm, which may be necessary to reduce oxygen inhibition and achieve suitably cured, i.e., non-tacky, surfaces. Oxygen inhibition occurs when oxygen present in the atmosphere quenches the reactive species produced by photoexcitation at the surface of the film to be cured.
Known nail films cured with UV-LED may therefore present one or more problems, such as defective surface curing and/or undesirable tackiness, leading to an unsatisfactory finished nail appearance and/or feel. To compensate for this deficiency, consumers traditionally apply a thicker coat of polish on the nail bed and, subsequent to curing, remove the tacky layer from the surface to reveal a hard film coating. In addition, U.S. Patent Application Publication No. 2005/234145, incorporated herein by reference in its entirety, discloses a process for photocuring thick layer (e.g., greater than 10 mils) ethylenically unsaturated systems with a LED light source using acylphosphine oxide photoinitiators. However, this process is useful only for thick gel coats, thick multi-ply composites, or thick adhesive layers. Such processes are not useful in the context of thin films, such as the application of a thin cosmetic film to a keratinous substrate, e.g., the nails. Further, U.S. Patent Application Publication No. 2010/160475, incorporated herein by reference in its entirety, discloses processes for photocuring thin layer (e.g., less than 10 mils) ethylenically unsaturated systems using a combination of an acylphoshpine oxide photoinitiator and an acrylated siloxane. However, such processes are time-consuming, requiring extended periods of LED radiation, which, as described above, is not suitable in the context of cosmetic applications. Also, the incorporation of additional components, such as acrylated siloxanes, serves to increase the overall production and consumer costs of such compositions.
Other methods for overcoming the inability of UV-LED to reduce oxygen inhibition have also been considered. For example, amines have been added to compositions that are to be cured using UV-LED. The amines readily undergo a chain peroxidation reaction which consumes oxygen that diffuses into the film. However, the presence of amines in the compositions may present various problems, such as yellowing of the cosmetic film, undesirable odors, plasticizing effects, softening of the cosmetic film coating due to the chain reactions, and/or decreased resistance of the cosmetic film to wear due to the formed hydroperoxides.
Other methods include application of a wax barrier coat or performing the UV-LED exposure under water to slow down the diffusion of atmospheric oxygen into the UV-curable composition. However, such methods may adversely affect the surface properties of the cosmetic film. Further, immersion in water may increase the risk of skin sensitization due to uncured monomers which may be present in the water in trace amounts. Another method involves performing the UV-LED exposure under inert conditions, which effectively overcomes oxygen inhibition, but is not a cost-effective or practical solution for nail enamel application.
Thus, there remains a desire to provide a photocurable cosmetic product that can be cured under UV-LED, which also makes it possible to more safely and/or more conveniently obtain a tack-free cosmetic film. It has now been surprisingly discovered that cosmetic compositions comprising (1) at least one ethylenically unsaturated polymerizable compound, and (2) a photoinitiator system, e.g., comprising (a) at least one photoinitiator having an absorption wavelength greater than about 350 nm, or (b) at least two photoinitiators wherein at least one photoinitiator has at least one absorption wavelength greater than about 350 nm, may yield tack-free, thin cosmetic films upon photocuring with UV-LED radiation, and may also significantly reduce curing times.